Git hooks: default patterns are used if no Kotlin files have changed

[mfederczuk]

This is a follow up to my PR #1606, concerning an oversight on my part.

In the new Git hooks, if git diff doesn't report any Kotlin files changed (which happens either because no Kotlin files are staged (pre-commit), or because no Kotlin files have been changed between HEAD and the remote branch (pre-push)) then ktlint will fall back to the default patterns, which match every file in the project — tracked in VC or not.

For some projects, this is undesirable, either because the codebase contains a lot of legacy code that isn't properly formatted or because the project contains generated code that doesn't conform to style conventions.

I have a couple ideas on how to solve this issue:

1. Add yet another new option --no-default-patterns. Then the hooks could be updated to:

   git diff --name-only -z --cached --relative -- '*.kt' '*.kts' | ktlint --relative --patterns-from-stdin='' --no-default-patterns

2. Disable the default patterns if the option --patterns-from-stdin is used, even if no patterns are given

3. Remove the default patterns outright

4. Reintroduce the xargs --no-run-if-empty hack:

   if [ "$(uname -s)" != "Darwin" ] then
       no_run_if_empty=--no-run-if-empty
   fi
   
   git diff --name-only --cached --relative -- '*.kt' '*.kts' | xargs $no_run_if_empty ktlint --relative

   Though this would also reintroduce the issues with that hack:

   • Pathnames with whitespace and/or special characters in it won't be found by ktlint (due to either xargs splitting them or git diff quoting them)
   • --no-run-if-empty is an extension of GNU xargs

---

For anyone else having this problem, a quick and dirty workaround for now would be to simply always give at least one file on the command line. For example:

git diff --name-only -z --cached --relative -- '*.kt' '*.kts' | ktlint --relative --patterns-from-stdin='' 'settings.gradle.kts'

[paul-dingemans]

At first glance, option 2 seems most attractive to me. Adding default patterns doesn't make sense in case you want to get them from stdin (regardless whether stdin is empty or not) anyways.

[paul-dingemans]

Solved by #1801